The regulatory role of thymus-derived (T) cells on the antibody response of chickens is being investigated by transfer experiments and other manipulations designed to deplete or augment specific populations of lymphocytes. The relationship of suppressor T cells to helper T cells is being studied with the objective of being able to easily differentiate the two populations. In addition, the postulated role of suppressor T cells in cell-mediated or T cell immune responses (i.e., allograft rejection, graft-versus-host reaction) is simultaneously being investigated. Through these latter studies, an attempt is being made to establish a reproducible assay system for enumerating suppressor cells. As an adjunct to these investigations, attempts are being made to physically separate various regulatory cell populations and study such populations morphologically and functionally. Finally, the potential role of regulatory T cells, especially those with a suppressive function, in the development of an autoimmune process will be studied using the spontaneous autoimmune thyroiditis occurring in obese strain chickens as a model. BIBLIOGRAPHIC REFERENCES: Moticka, E.J. 1975 Cellular basis and nature of the polyclonal hyperimmunoglobulinemia induced by antigenic challenge. Cell. Immunol. 19:32-40. Moticka, E.J. 1976, Regulatory role of thymocytes in the immune response. Fed. Proc., in press.